Thermal stability of poly(methyl methacrylate-co-butyl acrylate) and poly(styrene-co-butyl acrylate) modified with a small amount of acrylic acid and/or N-methylolacrylamide as a crosslinking agent was studied in this work. Programmed thermogravimetric analysis has been used to study the effect of copolymer composition on thermal stability, over a temperature range from 50 to 450 degrees C, under a constant now of nitrogen. Kinetic parameters of thermal degradation, activation energy, pre-exponential factor, and reaction order were obtained by using MacCallum-Tanner＇s approach. Kinetic data indicate that the thermal degradation of the investigated copolymer systems is the first order reaction, and that the increase of activation energy may be an indication of thermal stability changes in copolymer systems.